The oil industry has traditionally employed oil-soluble dimer acid based corrosion inhibitors to reduce corrosion in oil well piping. These inhibiting formulations commonly consist of materials which are produced by the thermal condensation of functionalized C.sub.18 fatty acids (containing one or two double bonds, e.g., oleic and linoleic, respectively). Examples of well known methods by which the thermal polymerization of fatty acids occur include heating an appropriate fatty acid mixture (e.g., tall oil fatty acid or soya fatty acid) in the presence of a clay or other suitable catalyst to give varying amounts of C.sub.36 (dimerized) and C.sub.54 (trimerized) fatty acids. These dimer and/or trimer fatty acids are neutralized with an appropriate amine (generally a diethylenetriamine, or DETA) derived fatty acid imidazoline to produce a corrosion inhibitor. These inhibitors are oil-soluble with minimum water dispersibility and act by coating metal surfaces (via adsorption by polar groups), thereby excluding the water which is necessary for the corrosion process to occur.
However, over the past few years several factors have caused the oil industry to reevaluate its traditional preference for oil-soluble water-dispersible corrosion inhibitors. Currently, many oil wells are producing mixtures higher in water content than in oil. Efficiency could be improved by utilizing the majority fluid in these wells as the carrier for the inhibitor. Also, water (and dissolved earth minerals) is the medium which causes electrochemical corrosion in oil and gas pipelines. If one could effectively disrupt the corrosion cycle at its source, one should have a more effective inhibitor. Finally, the carrier solvent constitutes about 70% of a standard corrosion inhibitor package. Replacing the traditional heavy aromatic napthas and other hydrocarbon solvents with water would eliminate the environmental damage caused by using hydrocarbon solvents--while also reducing costs.
Thus, the developing trend in the oil industry is to switch from oil-soluble delivery systems for corrosion inhibitors to water-soluble delivery systems. This is evidenced by the increasing number of companies which require corrosion inhibitors to be evaluated via linear polarization resistance meters (which test for inhibition in pure aqueous systems rather than the traditional hydrocarbon/aqueous systems).
In order to increase their water-dispersibility, conventional oil-soluble dimer/trimer mixtures have been coformulated with both fatty acid imidazolines and a variety of surfactants. However, this approach has proven limited in its scope. The use of enough surfactant to render the dimer/trimer molecule water-soluble results in drastically reduced film formation and film persistency. That is, the corrosion inhibitor simply washes-off the metal, leaving it unprotected. Also, these highly surfacted packages have a tendency to emulsify under downhole conditions, resulting in major problems for the user.
Water-soluble corrosion inhibitors which are currently available include alkyl pyridine quaternary compounds (generally benzyl quats), imidazoline salts (with acetic acid), and imidazoline ethoxylates. Although these inhibitors have found limited use in oil and gas pipelines, they have not yet proven tenacious enough to successfully inhibit corrosion when utilized under the dynamic downhole conditions prevalent in producing oil wells.
Therefore, it is the object of this invention to provide an effective and economical oil field corrosion inhibitor capable of being manufactured as either a highly water-dispersible molecule or as a water-soluble molecule. These molecules can be formulated to yield oil-soluble, highly water-dispersible corrosion inhibitor packages or oil-dispersible, water-soluble corrosion inhibitor packages, based upon the specific individual needs of the user. Other objects, features, and advantages will be evident from the following disclosures.